Archaeal Richmond Mine Acidophilic Nanoorganisms (ARMAN) were first discovered in an extremely acidic mine located in northern California (Iron Mountain Mine) by Brett Baker in Jillian F. Banfield's laboratory at the University of California Berkeley. These novel groups of Archaea named ARMAN-1, ARMAN-2, and ARMAN-3 were missed by previous PCR-based surveys of the mine community because the ARMANs have several mismatches with commonly used PCR primers for 16S rRNA genes. Baker et al detected them in a later study using shotgun sequencing of the community. The three groups represent three novel lineages within the Euryarchaeota, a subgroup of the Archaea. Their 16S rRNA genes differ by as much as 17% between the three groups. Prior to their discovery all of the Archaea shown to be associate with Iron Mountain belonged to the order Thermoplasmatales (eg. Ferroplasma spp.).
Examination of different sites in the mine using fluorescent probes specific to the ARMAN groups has revealed that they are always present in communities associated with acid mine drainage (AMD) that have pH < 1.5. They are usually found in low abundance (5-25%) in the community. More recently, closely related organisms have been detected in a boreal mire or bog in Finland .
Using cryo-electron tomography an extensive 3D characterization of uncultivated ARMAN cells within mine biofilms has been done (Comolli et al. in press). This has revealed that they are right at the cell size predicted to be the lower limit for life, 0.009 µm3 and 0.04 µm3 (NRC Steering group). Furthermore, the cells contains on average ~92 ribosomes per cell. This is astoundingly little when you consider that the average E. coli cell grown in culture contains ~10,000 ribosomes.
Filtration of the mine samples and examination using microscopy has revealed that they are very small cells (~300nm in diameter), possibly the smallest yet described that are free living. The genomes of these are groups have been been sequenced at the DOE Joint Genome Institute during a 2006 community sequencing program (CSP). Draft assemblies of the genomes are complete and their lifestyle is becoming well understood.